The invention relates to a gas laser tube, and more particularly to a structure for holding a cathode in a gas laser tube of the internal mirror type in which enclosure members of the gas laser tube are sealed with sealing flush members at opposite ends of the tube and provided with hollow members with spot facings. Glass face plates are provided at the spot facings of the hollow members.
Referring to FIG. 1, in a conventional gas laser tube of the internal mirror type, enclosure members of the gas laser tube comprise a thick glass tube 4, sealing flush members 1a and 1b, hollow members 2a and 2b with spot facings, and mirrors 10. The thick glass tube at its opposite ends is sealed with the sealing flush members 1a and 1b which are respectively provided with the hollow members 2a and 2b with the spot facings. The hollow members 2a and 2b are respectively provided with mirrors 10 at the spot facings. The sealing flush members 1a and 1b are respectively attached to the hollow members 2a and 2b by soldering. A gap between the hollow member and the mirror is sealed with a low melting point glass material 9. The hollow member 2b serves as an anode.
A conventional structure for mounting the cathode to the enclosure members in the gas gas laser tube will be described. The tube type cathode made of aluminum is attached at a welding region 14 to the sealing flush member 1a by welding. The enclosure members at the anode side are provided with a discharge chamber 8 which is provided with an outlet for releasing a gas within the discharge chamber 8. A slender discharge tube 7 at the anode side is attached to a wall of the discharge chamber 8. The thick glass tube 4 and the slender discharge tube are formed as an integral structure through the wall of the discharge chamber 8. The thick glass tube 4, the cathode 5 and the slender discharge tube 7 are arranged coaxially.
In the conventional structure for holding the cathode in the gas laser tube of the internal mirror type as shown in FIG. 1, the cathode 5 is attached to the sealing flush member 1a only by means of a resistance welding. The sealing flush member la is made of Kovar (Fernico). In contrast, the cathode 5 is made of aluminum. The sealing flush member has an electrical resistance higher than that of the cathode. Consequently, when the sealing flush member 1a is subjected to the resistance welding, the welding region 14 of the sealing flush member 1a has a tendency of melting or cracking, causing leaks. Assuming that the welding for attaching the cathode 5 to the sealing flush member 1a is carried out with a low welding current, the strength of the attachment of the cathode 5 to the sealing flush member 1a is so weak as to tend to pull out the cathode from the sealing flush member 1a.
On the other hand, an alternate conventional structure for mounting the cathode to the enclosure members in the gas gas laser tube will be described. Referring to FIG. 2, the cathode 5 at its top portion is provided with a slender projection. The hollow member 2a attached to the sealing flush member 1a is formed at its hollow portion with a ring-shaped groove 13. The slender projection of the cathode is inserted into the hollow member 2a and caulked with the ring-shaped groove 13 formed in the hollow member 2a so as to hold the cathode in the gas laser tube.
In such a structure for holding the cathode, the cathode 5 may be held to the enclosure members of the gas laser tube without welding, the gas laser tube therefore does not have the problems of melting or cracking of the sealing flush member by welding. The cathode is, however, attached to the sealing flush member only by the caulking of the slender projection of the cathode with the ringshaped groove in the hollow member. In operation of the gas laser, the cathode and the hollow member are subjected to vibrations and thermal expansion. Thus, the caulking of the slender projection of the cathode tends to loosen or the cathode tends to pull out from the sealing flush member.